1. Field of the Invention
The present invention relates to a method used in a wireless communication system and related communication device, and more particularly, to a method of handling interference mitigation in a heterogeneous network by performing channel measurement and related communication device.
2. Description of the Prior Art
A long-term evolution (LTE) system supporting the 3GPP Rel-8 standard and/or the 3GPP Rel-9 standard are developed by the 3rd Generation Partnership Project (3GPP) as a successor of a universal mobile telecommunications system (UMTS), for further enhancing performance of the UMTS to satisfy increasing needs of users. The LTE system includes a new radio interface and a new radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes multiple evolved Node-Bs (eNBs) for communicating with multiple UEs, and communicates with a core network including a mobility management entity (MME), a serving gateway, etc., for Non Access Stratum (NAS) control.
A LTE-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at the coverage edge of an eNB, and includes advanced techniques, such as carrier aggregation (CA), coordinated multipoint transmission/reception (CoMP), UL multiple-input multiple-output (MIMO), etc. For a UE and an eNB to communicate with each other in the LTE-A system, the UE and the eNB must support standards developed for the LTE-A system, such as the 3GPP Rel-10 standard or later versions.
In addition to the advanced techniques mentioned above, the most effective way for improving quality of a received signal is to shorten a distance between a transmitter and a receiver in a wireless communication system. Thus, a heterogeneous network is proposed for introducing multiple layers of cells in the wireless communication system such that the distance between the transmitter and the receiver is shortened. For example, there are three types of cells and a relay node in the heterogeneous network. According to sizes of the cells, the cells are a macrocell, a picocell and a femtocell from the largest to the smallest. Besides, the macrocell, the picocell and the femtocell are managed by a macrocell base station (BS), a picocell BS and a femtocell BS, respectively. Different from a convention network including only macrocells, the heterogeneous network not only includes the macrocells, but each of the macrocells includes at least one picocell, at least one femtocell and at least one relay node for improving throughput of UEs in the heterogeneous network. In this situation, a UE in coverage of a macrocell may also be in coverage of a picocell or a femtocell in the macrocell. If the UE is near a picocell BS of the picocell or a femtocell BS of the femtocell and is far from a macrocell BS of the macrocell, the UE can communicate with the picocell BS or the femtocell BS with low transmission power to access services such as Internet, TV broadcasting, etc. Even if the UE is not in the coverage of the picocell and the femtocell, the UE may also communicate with the macrocell BS via a relay node which is near the UE. That is, the relay node serves as a bride between the UE and the macrocell BS, and forwards signals between the UE and the macrocell BS. In other words, the UE and the macrocell BS do not need to increase their transmission power greatly to communicate with each other. Therefore, power consumption of the UE and the macrocell BS can be reduced by using the picocell BS, the femtocell BS or the relay node. Furthermore, throughput of the UE is increased since quality of the signals transmitted and received by the UE is improved due to a short distance between the UE and the picocell BS, the femtocell BS or the relay node.
However, even though the power consumption of the UE and the macrocell BS is reduced, interference in the macrocell is increased since the picocell BS, the femtocell BS and the relay node may transmit and receive signals at the same time in an overlapped bandwidth and cause the interference to each other. Furthermore, since orthogonal frequency-division multiplexing (OFDM) and orthogonal frequency-division multiple access (OFDMA) adopted in the LTE system and the LTE-A system are wideband techniques, signals processed by the OFDM or the OFDMA are transmitted and received in any part of a bandwidth. That is, the picocell BS, the femtocell BS and the relay node may transmit and receive the signals in any part of the bandwidth at a given time. It is highly possible that the signals are transmitted and received in the same part of the bandwidth at the given time, i.e., the same resource block, and the signals interfere with each other. Thus, the interference in the macro cell becomes much severer in the LTE system and the LTE-A system. Benefit introduced by the heterogeneous network can not be realized efficiently. That is, an amount of the throughput of the UE that can be increased is limited due to the interference. Therefore, it is important to take the interference introduced by the heterogeneous network into consideration before arranging resource to the UE, to increase the throughput of the UE greatly.